The union of sperm and egg at fertilization is an essential step in reproduction and development. In mammals, including human, sperm must first bind to the egg's zona pellucida coat and complete the acrosome reaction before fusing with the egg. The zona pellucida initiates acrosome reactions by triggering the entry of calcium ions into sperm through TRPC cation channels. However, the downstream mechanisms that couple calcium signals into the final events of the acrosome reaction are poorly understood and represent a major gap in our understanding of fertilization. We discovered a novel TRPC binding protein, enkurin, in sperm. The objective of this project is to delineate the roles of enkurin in sperm function. The working hypotheses for this stage of the project is that enkurin is an adaptor that acts by tethering regulatory molecules to the TRPC channel, and that these regulatory molecules play essential roles in the initiation of the acrosome reaction. These hypotheses will be tested in experiments that: (i) map interaction sites on enkurin for TRPC channels and a regulatory kinase that mediate binding and functional activity; (ii) identify products of the activated regulatory kinase in sperm; (iii) determine the downstream consequences of enkurin/kinase activation in control of acrosome reactions; (iv) determine, the mechanism by which enkurin regulates TRPC ion channel activity; and (v) determine the mechanism of enkurin action in transgenic mice. These studies are relevant in two regards. First, they may advance our basic understanding of an essential step in the reproductive process. Second, there may be therapeutic consequences to these studies both with regard to the treatment of human infertility and for the design of new contraceptives.